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seen Jan 20 at 16:16

Feb
11
comment Pareto efficiency and Standard Model parameters
What do you mean for a parameter to be 'better' or 'worse' off? Perhaps more attuned for life?
Jan
16
awarded  Yearling
Jan
4
comment does the background spacetime of a black hole affects its thermodynamic properties?
In AdS space, every large black hole is eternal. See hep-th/0106112.
Dec
19
answered does the background spacetime of a black hole affects its thermodynamic properties?
Dec
10
comment To which extent is general relativity a gauge theory?
In general the rule of thumb is that you CAN make the analogy with relatively robust, modulo some small details.. Like the fact that the primary variables are first order in the YM gauge fields, whereas in GR the primary variables are 2nd order.
Dec
10
comment To which extent is general relativity a gauge theory?
One of the confusing things here is that there are several somewhat related but different formalisms of GR whereby you can sort of make the analogy between YM gauge fields and GR. The exact gauge group is sometimes GL(n,R) sometimes SL(2,C) and sometimes Diff(M). The earliest version I know was written by Utiyama, and later by Sciama-Kibble and others. Meanwhile particle physicists work in the linearized approximation, where the equivalence is manifest
Dec
7
answered What is background independence and how important is it?
Nov
29
comment Assuming SUSY is found to be incorrect, what would then be the most compelling candidates for dark matter?
There are plenty of logical alternatives that are independent of supersymmetry. Almost any weakly interacting particle that isn't too heavy to freeze out in the early universe will do (eg those arising from little higgs models for instance). Many of these haven't quite been ruled out yet at the LHC. Axions as one of the answers below is another popular and consistent alternative, more generally condensates of many forms. And there are other ideas as well, eg primordial black holes or modifying gravity etc.
Nov
28
answered Why is it desirable to have a symmetry to make cosmological constant zero?
Nov
21
comment Is String Theory formulated in flat or curved spacetime?
This doesn't really have anything to do with string theory. Your question is more a long the lines of how can a linearized field theory look like a full nonlinear geometric theory? The answer and procedure takes quite a few pages to write down, but mathematically its actually very much like what happens with nonabelian gauge theory where you can ask a similar question. eg "how can gluons be quanta". In the case of gravity, unfortunately the whole story has been obfuscated by a group of people who confuse themselves needlessly (possibly for historical reasons) but it really is quite simple
Nov
6
comment What constitutes an observation/measurement in QM?
Lubos, are you saying that one observer will measure one track of an electron in a bubble chamber, and another observer can potentially measure another direction? If so, I definitely disagree. It is precisely b/c of quantum mechanics that ALL observers objectively agree on the direction of the track.
Oct
9
comment How can perturbativity survive renormalization?
Your question is very much at the heart of renormalization, and with all due respect to the answers below, really deserves a textbook treatment. The typical regularization and renormaliztion scheme and book treatment seems a bit magical at first, but it makes perfect sense once you get to the renormalization group and Wilsonian treatment where the approximation makes more sense
Oct
7
comment How can perturbativity survive renormalization?
This is the subject of almost any QFT textbook, and is way outside the scope of a few paragraphs. For a renormalizable theory, each infinity is pushed off into the next order, leaving only finite pieces
Oct
6
comment What is the easiest way to stop a star?
Indeed, you'd need an efficient way to remove heavier elements from a star's surface, which is difficult as you'd have to pass through the Corona. Getting the hydrogen to circulate is yet another problem.
Sep
21
comment What is the easiest way to stop a star?
Right. It strikes me as much more energetically efficient to actually gather hydrogen from nearby astrophysics sources and bring them back to the sun for fuel. Coupled with a suitable Dyson sphere, you would have amongst the more efficient (in the Carnot sense) stellar factories that you could think off. Fusion on the human scale will never be as efficient as what goes on in the sun.
Sep
9
comment de sitter cosmologic limit
This answer is problematic and nonstandard. There are parts that are correct, parts that are false and parts that are pure speculation. Its better to keep things ordered by what happens classically, semiclassically and then in specific proposals of QG. Therefore I prefer Lubos' answer
Aug
17
comment What nonstandard theory forbids quantum computers?
I'm not so sure about 'fundamental decoherence' If you really treat those noise terms as fundamental, rather than some effective thermodynamic limit, you violate unitarity and thus one of the assumptions of the CPT theorem fails. You thus can't 'break' CPT, it doesn't even exist as an operator!
Aug
17
comment Why do people categorically dismiss some simple quantum models?
Do you have a simple CA model that exhibits superselection?
Aug
17
comment What nonstandard theory forbids quantum computers?
What do you mean by the phrase 'break CPT in decoherence'...
Jun
8
awarded  Caucus